Preparation And Application In High Thermal Conductive Composites Of Aluminium Nitride Microspheres

At present,electrical and electronic devices are becoming lighter,smaller size,higher integration and higher power output,which require the electronic packaging to have excellent overall performances besides high thermal conductivity.Thermal insulation materials have attracted more and more attention because of their excellent performances such as corrosion resistance,low cost,light weight,easy processing,low energy consumption,good electrical insulation performance.In this paper,we studied the preparation process of the aluminum nitride(AIN)microspheres,the influence of surface modification,filler content,multi-walled carbon nanotubes and polymer matrix on the properties of high thermal conductivity insulating composites in which the aluminum nitride microspheres were used as fillers.We provided an effective and facile synthesis route of AIN microspheres via combining sol-gel technique and gas reduction nitridation method.The influence of PO addition amount,various surfactants on the morphology of AIN microsphere precursor has been studied.The results showed that PO accelerated the gelation reaction,and the precursor microspheres could be obtained when the PO addition amount was in the range of 7 ml to 9 ml.The size of aluminum nitride precursors could be increased by addition of surfactants such as ammonium sulfate,ammonium chloride,sucrose,citric acid,PEO-PPO-PEO and polyethylene glycol,and the addition of CTAB resulted in a decrease in the particle size of the aluminum nitride precursors.We proposed solution mixing and hot pressing method to prepare KH550-AIN/UHMWPE composites by using ultra-high molecular weight polyethylene(UHMWPE)as the polymer matrix and modified aluminum nitride microspheres(KH550-AIN)as the filler.The effects of filler content on the thermal stability.thermal conductivity,mechanical properties and electrical insulation properties of KH550-AIN/UHMWPE composites were investigated.Thermal analysis showed that the addition of AIN increased the melting point and thermal decomposition temperature of the composites,but the crystallinity decreased slightly.The thermal conductivity results revealed that the composites filled with synthesized aluminum nitride microspheres had higher thermal conductivity,and the thermal conductivity of KH550-AIN/UHMWPE composites increased by adding KH550-AIN microspheres,and the thermal conductivity of the composites improved obviously when the filler content was higher than 30 wt%.The tensile strength and elongation at break of the composites decreased with the increase of aluminum nitride.The electrical insulating tests indicated that the dielectric constant of the composites was less than 7,and the dielectric loss was in the order of 10'2,and the surface and volume resistivity were above the order of 1014 in the full range of KH550-AIN addition,which indicated that the composites had good electrical insulation properties and can be used as insulating materials.Polydopamine had been introduced to the surface of MWCNT to obtain the PDA-MWCNT.Then 1 wt%of PDA-MWCNT was added to 40 wt%KH550-AIN filled UHMWPE composites to get PDA-MWCNT/KH550-AIN/UHMWPE composites.The structure and morphology of PDA-MWCNT were characterized by SEM,TEM,FTIR,TG and XPS.The thermal conductivity and tensile properties of PDA-MWCNT KH550-AIN/UHMWPE were also measured.The results revealed that PDA was successfully coated on the surface of MWCNT and PDA-MWCNT had good interfacial compatibility with KH550-AIN/UHMWPE composites.The thermal conductivity and tensile strength of PDA-MWCNT/KH550-AIN/UHMWPE composites were higher than those of KH550-AIN/UHMWPE composites.Polystyrene(PS),high density polyethylene(HDPE),polyphenylene sulfide(PPS)and polyamide 6(PA6)composites were prepared by adding 60 wt%KH550-AIN or 60 wt%PDA-Al2O3,and the thermal conductivity of the composites was studied.The results showed that the polymer matrix played a very important role in the preparation of high thermal conductivity composites.The thennal conductivity of the composites was in the order of PA6>HDPE>PPS>PS,and the corresponding thermal conductivity was 1.85,1.41,0.95 and 0.84 W · m-1·K-1 respectively.